With a time-of-flight mass spectrometer, different ions that are accelerated at substantially the same time by an electrical field are introduced into a flight space that is formed in a flight-tube. The time of flight required for the ions to reach an ion detector after traveling through the flight space is used to separate the different ions by mass (to be more accurate, by mass-to-charge ratio, m/z). The ion detector converts the time of flight to mass so that a continuous signal is detected corresponding to the quantity of ions that reach the ion detector. A mass spectrum is then created where the horizontal axis is used as the mass axis, and the vertical axis is used as the signal strength axis. With a time-of-flight mass spectrometer such as this, mechanical expansion and contraction of the flight-tube caused by changes in temperature cause subtle changes in the flight distance of the ions. These subtle changes in the flight distance cause variations in the flight time of ions of the same mass. This then causes a shift in the mass axis of the mass spectrum. If the temperature change (temperature drift) of the flight-tube is large enough, the shift in the mass axis can cause an error in the accuracy of the measured mass to exceed the required specifications for the apparatus. For this reason, with the time-of-flight mass spectrometer described in Patent Literature 1, variations in temperature of the flight-tube 17 are reduced by the use of a system for controlling the temperature of a vacuum chamber 10 wherein the vacuum chamber that houses flight-tube 17 made of stainless steel is disposed within a constant temperature chamber 15 as shown in FIG. 4 and the temperature within the constant temperature chamber 15 is monitored with a temperature sensor 32 to control the temperature of the vacuum chamber 10. However, even if the temperature of the vacuum chamber is controlled, if the ambient temperature (the temperature of the room where the apparatus is installed) changes rapidly, it is difficult for the temperature adjustment and control for the vacuum chamber to keep up with the change in the ambient temperature, causing temperature disturbances that result in the mass axis to shift.
Prior Art Literature
Patent Literature
    Patent Literature 1: Laid-Open Patent Application Publication No. 2008-157671